The Liquid Crystal Display (LCD) possesses advantages of thin body, power saving and no radiation to be widely used in many application scope. It has been widely utilized in, such as mobile phones, PDAs (personal digital assistance), digital cameras, laptop screens or notebook screens.
Most of the liquid crystal displays on the present market are back light type liquid crystal displays, which comprise a shell, a liquid crystal display panel located in the shell and a backlight module located in the shell.
Generally, the structure of the LCD panel mainly comprises a Color Filter (CF), a Thin Film Transistor Array Substrate (TFT Array Substrate) and a Liquid Crystal Layer filled inbetween. The working principle is that the light of backlight module is reflected to generate images by applying driving voltages to the two glass substrate for controlling the rotations of the liquid crystal molecules.
For aligning the liquid crystal molecules more regular, an over coat layer with alignment process are respectively provided to the sides of the CF substrate and the TFT substrate close to the Liquid Crystal Layer. The acting force between the branched groups in the alignment layer after process and the liquid crystal molecules is stronger and the anchoring function is provided to the liquid crystal molecules to align the liquid crystal molecules tilting relative to the surface of the alignment layer with a polar angle. The polar angle is the pre-tilted angle of the liquid crystal molecules. The pre-tilted angle can control the alignment of the liquid crystal molecules to prevent the appearance of anti-dumping domains and thus, to optimize the display effect. In the manufacture process of the liquid crystal display panel, the alignment process to the alignment layer is an important process to realize that the liquid crystal molecules to be aligned according to the specific direction and angle by the alignment process. Mainly, rubbing is the main means of the alignment method of the alignment layer according to prior art.
The traditional liquid crystal display panel comprises a plurality of pixels alignment in array, and each pixel comprises a red (R), a green (G), a blue (B), three sub pixels. The R, G, B color resists utilized in prior art are all absorption type color resists. When the light is incoming, only the light of corresponding color can permeate, the lights of other two colors are both absorbed, which make the transmission of the display panel is lower. Therefore, the display technology of forming red, green, blue, white, four sub pixels in one pixel appears. No color resist is added to the W sub pixel to allow more backlight to permeate. Accordingly, the transmission and the brightness of the liquid crystal display panel can be promoted.
The benefit of the RGBW is to promote the usage ratio of the backlight to save the power consumption and lower the cost. The higher brightness level can be achieved under the condition that resolution is not decreased and the power consumption is increased. However, as shown in FIG. 1, at the side of the CF substrate 100 of the liquid crystal display panel, the RGB sub pixels will use the color resists of the same thickness and W sub pixel does not have the color resist. Thus, after coating an alignment layer 120 on the respective pixels and a black matrix 110 overall, the portion of the alignment layer 120 correspondingly covering the W sub pixel appears a sunk area, and the sunk area makes the surface of the alignment layer 120 uneven. As the single rubbing according to prior art is employed to implement the rubbing alignment process to the alignment layer 120, the dead corners where the rubbing roller 300 cannot rub generates at the backside of the sunk area along the rubbing direction, and thus rubbing shadow 130 exists. Namely, the rubbing alignment process is not implemented to the area corresponding to the rubbing shadow 130. Consequently, the liquid crystal alignment in the rubbing shadow 130 is disorientated. Thus, the light leakage issue of the liquid crystal display panel in the dark state occurs and the contrast ratio of the liquid crystal display panel is degraded.